var arr = [1,2,3.14,'Hello',null,true];
console.log(arr.length);

var arr =[1,2,3];
console.log(arr.length);
arr.length=6;
console.log(arr);
arr.length=2;
console.log(arr);

var arr=['A','B','C'];
arr[1]=99;
console.log(arr);

var arr=[1,2,3];
arr[5]='x';
console.log(arr);

var arr=[10,20,'30','ljy'];
console.log(arr.indexOf(10));
console.log(arr.indexOf(20));
console.log(arr.indexOf(30));
console.log(arr.indexOf('30'));

var arr=['A','B','C','D','E','F','G'];
console.log(arr.slice(0,3));
console.log(arr.slice(3));

var arr=['A','B','C','D','E','F','G'];
var brr=arr.slice();
console.log(brr);
brr===arr;